Peracids have been used for disinfection in a number of applications. U.S. Pat. No. 6,545,047 B1 describes a method for sanitizing animal carcasses using antimicrobial compositions containing one or more peracids. U.S. Pat. No. 6,183,807 B1 describes a method for cleaning and sanitizing meat products using antimicrobial compositions containing one or more peracids. U.S. Pat. No. 6,518,307 B2 describes a method for controlling microbial populations in the gastrointestinal tract of animals by orally administering an effective amount of peracid. U.S. Patent Appln. Pub. No. 20030026846 A1 describes a method of using peracid/acid compositions to control pathogenic organisms on living plant tissue. U.S. Pat. No. 5,683,724 describes a process for preventing microbial growth in aqueous streams used for transporting or processing food products and packaged foods that uses an effective antimicrobial concentration of peracid.
Peracids can be prepared by the chemical reaction of a carboxylic acid and hydrogen peroxide (see Organic Peroxides, Daniel Swern, ed., Vol. 1, pp 313-516; Wiley Interscience, New York). The reaction is usually catalyzed by a strong inorganic acid, such as concentrated sulfuric acid. The reaction of hydrogen peroxide with a carboxylic acid is an equilibrium reaction, and the production of peracid is favored by the use of an excess concentration of peroxide and/or carboxylic acid, or by the removal of water. There are several disadvantages to the chemical reaction for peracid production: a) the high concentration of carboxylic acid used to favor production of peracid can result in an undesirable odor when using the peracid-containing solution, 2) the peracid is oftentimes unstable in solution over time, and the concentration of peracid in the solution decreases during storage prior to use, and 3) the formulation is often strongly acidic due to the use of a concentrated sulfuric acid as catalyst. One way to overcome the disadvantages of the chemical production of peracids is to employ an enzyme catalyst in place of a strong acid catalyst. The use of an enzyme catalyst allows for the rapid production of peracid at the time of use, avoiding the problem of storage of peracid solutions and of using chemically-produced peracid solutions containing an unknown concentration of peracid. The high concentrations of carboxylic acids typically used to produce peracid via the direct chemical reaction with hydrogen peroxide are not required for enzymatic production of peracid, where the enzyme-catalyzed reaction can use a carboxylic acid ester or amide as substrate at a much lower concentration than is typically used in the chemical reaction. The enzyme reaction can be performed across a broad range of pH, dependent on enzyme activity and stability at a given pH, and on the substrate specificity of the enzyme for perhydrolysis at a given pH.
Enzymes can catalyze the perhydrolysis of esters and amides to produce the corresponding peroxycarboxylic acids (Equations 1 and 2), however, most known methods for preparing peracids from the corresponding carboxylic acid esters or amides using enzyme catalysts do not produce and accumulate a peracid at a sufficiently-high concentration to be efficacious for disinfection in a variety of applications,

The use of hydrogen peroxide as an enzyme substrate for the enzymatic perhydrolysis of carboxylic acid esters or amides can be problematic, as hydrogen peroxide is known to oxidatively inactivate numerous enzymes (M. R. Gray, Biotech Adv., 7:527 (1989)). K. Kleppe (Biochemistry, 5:139 (1966)) report that hydrogen peroxide inactivates enzymes by modifying certain amino acid residues in proteins, where at acid pH values methionine is easily oxidized to methionine sulfoxide, and at basic pH values tryptophan is destroyed. D. A. Estell et al., (J. Biol. Chem., 260:6518 (1985)) describe inactivation of enzymes containing methionine, cysteine or tryptophan residues by hydrogen peroxide, and demonstrate >80% inactivation of the protease subtilisin from Bacillus amyloliquefaciens in less than 6 minutes or 4 minutes using 0.1 M or 1.0 M hydrogen peroxide, respectively. Inactivation of peroxidases by 5 mM to 50 mM hydrogen peroxide is reported by M. B. Arnao et al., (Biochim. Biophys. Acta, 1041:43 (1990)), and B. Vaiderrama et al. (Chemistry & Biology, 9:555 (2002)) review the inactivation of peroxidases by oxidative species such as hydrogen peroxide. P. F. Greenfield et al. (Anal. Biochem., 65:109 (1975)) report an increase in inactivation of glucose oxidase with increasing hydrogen peroxide concentration. For the conversion of cephalosporin C to 7-aminocephalosporanic acid, both a D-amino acid oxidase and a glutaryl acylase were inactivated by the byproduct hydrogen peroxide produced by the oxidase (F. Lopez-Gallego, et al., Adv. Synth. Catal., 347:1804 (2005)). In view of these and other teachings, previously reported methods for enzymatic production of peracid utilize low concentrations of added hydrogen peroxide, where a low concentration of hydrogen peroxide would be expected to reduce or limit enzyme inactivation during the perhydrolysis reaction.
U.S. Pat. No. 3,974,082 (“the '082 patent”) describes the production of bleaching compositions for laundry detergent applications by contacting the material to be bleached with an aqueous solution containing an oxygen-releasing inorganic peroxygen compound, an acyl alkyl ester, and an esterase or lipase capable of hydrolyzing the ester. The bleaching compositions cited in the '082 patent are highly alkaline (using such buffering agents as pentasodium tripolyphosphate or sodium carbonate), and no data is presented for either the concentration of peracids produced in the cited compositions, or for the utility of the cited compositions for bleaching of laundry. The bleaching compositions cited in the '082 patent contain up to 40% by weight of per-compound, for example, hydrogen peroxide or alkali metal salts of percarbonate, perborate, persilicate and perphosphate. The bleaching compositions are added to water in amounts up to 12.5 grams per liter of water to initiate the enzyme-catalyzed perhydrolysis reaction, where the maximum concentration of hydrogen peroxide present in the enzyme-catalyzed perhydrolysis reaction is 5 grams/liter, equivalent to ca. 147 mM hydrogen peroxide.
U.S. Pat. No. 5,296,161 (“the '161 patent”) describes an activated oxidant system providing enhanced stain removing ability in both high and low temperature wash applications. The oxidant system is capable of in situ generation of >0.1 ppm peracid by enzymatic perhydrolysis, where in the absence of added enzyme the ester substrate is incapable of substantial chemical perhydrolysis. The oxidant system uses a source of peroxygen, a lipase or esterase, and glycerides or monoacylated ethylene glycol or propylene glycol derivatives to generate peracid. The most-preferred enzyme substrate in the '161 patent oxidant system is either trioctanoin or tridecanoin, the enzymatic reaction is carried out at a pH of from 7.5 to 11.0, and none of the accompanying examples demonstrate the production of greater than 10 ppm of peracid. The highest concentration of hydrogen peroxide present in the exemplified perhydrolysis reactions was 1314 ppm, equivalent to ca. 38.6 mM H2O2.
U.S. Pat. No. 5,364,554 describes an activated oxidant system for in situ generation of peracid in aqueous solution using a protease enzyme, a source of hydrogen peroxide, and an ester substrate that is preferably chemically non-perhydrolyzable. A method of bleaching and a method of forming peracid are also disclosed. The enzymatic reactions are carried out at a pH of from about 8.0 to 10.5, and none of the accompanying examples demonstrate the production of greater than 5 ppm of peracid. The concentration of hydrogen peroxide present in the exemplified perhydrolysis reactions was 400 ppm, equivalent to ca. 11.8 mM H2O2.
O. Kirk et al. (Biocataysis, 11:65-77 (1994)) investigated the ability of hydrolases (lipases, esterases, and proteases) to catalyze perhydrolysis of acyl substrates with hydrogen peroxide to form peroxycarboxylic acids, and reported that perhydrolysis proceeds with a very low efficiency in aqueous systems. Furthermore, they found that lipases and esterases degraded percarboxylic acid to the corresponding carboxylic acid and hydrogen peroxide. They also found that proteases neither degraded nor catalyzed perhydrolysis of carboxylic acid esters in water. The authors concluded that esterases, lipases and proteases are, in general, not suitable for catalyzing perhydrolysis of simple esters, such as methyl octanoate and trioctanoin, in an aqueous environment.
The problem to be solved is to provide an aqueous enzymatic process for in situ production of peracid compositions under neutral to acidic conditions from non-toxic and inexpensive carboxylic acid esters, amides, and/or glycerides at concentrations suitable for use as a disinfectant in a variety of applications. Preferably, the process will produce a concentrated aqueous solution of peracid within at least about 5 minutes. As such, the enzymatic perhydrolysis process should occur in the presence of at least 500 mM hydrogen peroxide (peroxygen source). It has been reported that for certain disinfecting, cleaning or bleaching applications a non-alkaline peracid solution is preferred. As such, the process should produce an aqueous peracid solution in a single step under neutral to acidic conditions, more preferably under acidic conditions. The process preferably needs to produce peracid compositions comprised of at least 10 ppm peracid (for example peracetic acid), more preferably at least 100 ppm, and even more preferably in the range of about 100 to about 5000 ppm, where the resulting peracid composition can be used directly, or diluted to the desired concentration of peracid prior to use, to produce a 5-log or 6-log reduction in the concentration of the targeted infectious microorganism in about 5 minutes to about 10 minutes, at temperatures ranging from about 0° C. to about 60° C., preferably about 4° C. to about 30° C., most preferably about 10° C. to about 25° C.
A second problem to solve is to provide a process to produce a multi-functional composition that has disinfecting, bleaching and prion-degrading activity. The process should produce an aqueous peracid solution in situ comprising a sufficient disinfecting and/or bleaching concentrations of peracid and one or more prion-degrading proteases.
An additional problem to be solved is the lack of a combination of enzyme catalyst and enzyme substrate that results in the conversion of carboxylic acid esters or amides to percarboxylic acid at a concentration more efficacious for bleaching in laundry applications, compared to the concentrations of peracids previously disclosed in the prior art. A solution to the problem needs to 1) efficiently produce an aqueous solution of peracid where the peracid is present in sufficient concentration to act as a disinfectant or bleaching agent, 2) use an enzyme catalyst having suitable perhydrolase activity for converting carboxylic acid esters, amides, and/or glycerides to the corresponding peracids in aqueous solution; 3) provide methods to improve catalyst stability to increase the catalyst productivity, thereby decreasing catalyst cost; and 4) provide methods to efficiently and economically obtain peracids from relatively inexpensive and non-toxic starting materials.